Halichondria panicea

Halichondria panicea, commonly known as the breadcrumb sponge, is a species of marine demosponge belonging to the family Halichondriidae. This is an abundant sponge of coastal areas of the North Atlantic and the Mediterranean Sea ranging from the intertidal zone to a recorded depth of over 550 m. It is very tolerant of a wide range of coastal habitats, including strong currents, high salinity and exposure to powerful wave action. Its only requirement is a rocky substrate which can include small cobbles.

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Morphology

Close-up view.

Halichondria panicea occurs in a very wide range of forms and can be difficult to identify. Some forms have a granular surface which gives rise to the common name but sometimes the surface is smooth, even glassy. The surface is often marked with pores (osculae) which can extend into tubular "chimneys" in wave-sheltered habitats. The overall form is determined largely by the habitat: wave-exposed forms usually form thin widespread sheets but wave-sheltered forms often form massive encrustations up to 20 cm thick. This diversity has led to its being described as a new species 56 times.[2]

The colour is also variable. The "natural" colour is cream or grey: this is usually found in specimens from relatively deep water. However at shallower depths, the sponge is usually green due to symbioticalgae which live close to the surface of the sponge. At intermediate depths the sponge tends to be green in summer, cream or grey in winter. It smells like "exploded gunpowder".[3]